Upgrading a naphtha by separation into two fractions and separate treatment of each fraction



SeP'f- 19, 1961 E. R. cHRlsTENsEN ET AL 3,000,810

RATION INTO TWO FRACTIONS UPGRADING A NAPHTHA BY SEPA AND SEPARATE TREATMENT OF EACH FRACTION Filed July :5, 1957 This invention relates to the treatment of hydrocarbons, and more particularly, to the upgrading of naphtha fractions. In one of its more specific aspects the invention is concerned with the production of high octane motor fuels.

Naphtha fractions are those normally liquid hydrocarbon fractions boiling up to about 425 F. and are composed of a mixture of paraiiins, oleiins, naphthenes and aromatics. Naphthas may be obtained from various sources. For example, straight `run naphtha is obtained by the fractional distillation of a crude petroleum. Thermally cracked land catalytically cracked n-aphthas are those fractions obtained from the thermal or catalytic cracking of heavier stocks. The octane numbers of the naphthas obtained from different sources vary considerably. Straight run naphtha for example, has an ASTM research octane number ranging from 40 to 67 clear and 62 to 83 leaded (containing 3 cc. TEL per gallon). The corresponding octane numbers of thermally cracked naphtha range from 75 to 84 clear and 85 to 93 leaded whereas the octane numbers of oatalytically cracked naphtha range from 89 to 93 clear and 94 to 97 leaded.

It is an object of this invention to provide a method for the upgrading of a naphtha fraction. Another object is to produce a motor fuel of high octane number. Another object is to produce a motor fuel of reduced sulfur content. Other objects will be apparent to those skilled in the art vfrom the following disclosure.

According to the invention the naphtha is fractionated to remove a light overhead fraction boiling up to about 210 F. The heavy fraction is then subjected to the action of a zinc oxide-zinc chrornite catalyst optionally in the presence of hydrogen. The so-treated heavy fraction is then combined with the light fraction to provide a motor fuel of increased octane number. The invention also contemplates additional treatment of the light naphtha to yield a final product of increased octane number.

The catalyst used for the treatment of the heavy fraction is a zinc oxide-zinc chromite catalyst, the zinc oxide being present in amounts ranging from l-90% based on the combined weight of the zinc oxide and zinc chromite. The zinc oxide-Zinc chromite catalyst may be used alone or may be deposited on a substantially inert base. Catalysts containing -75% zinc oxide based on the combined weights of zinc oxide and zinc chromite are preferred.

The catalyst m-ay :be prepared in the following manner. A rst solution was prepared by dissolving 3.036 parts by weight of C.P. ammonium dichromate in l0 parts by weight of water and adding 2.4 parts by weight of concentrated ammonium hydroxide in 4 parts of water. A second solution was prepared by dissolving 7.134 parts of C.P. Zn(NO3)2.6l-l20 in 16 parts of water. The first and second solutions were then mixed by being added slowly and simultaneously at equal rates with good `ragitation to ya vessel containing 4 parts of water. Stirring was continued for 1/2 hour after the addition was complete and then 6 parts concentrated ammonium hydroxide was `added to insure complete precipitation.

The precipitate was ltered and washed three times 3,00l0 Patented Sept. i9, 1961 with l0 parts of water, dried and the dried powder decomposed in small portions by heating to incipient decomposition temperature. The decomposition temperature was found to be about 640 F. The decomposed powder was then sieved through 20 mesh, pelleted in im inch dies with 2% Sterotex (a hydrogenated vegetable fat) and calcined at 750 F. for l2 hours. 2.85 parts of dark brown pellets were obtained.

The resultant catalyst contains 26% zinc oxide and 74% zinc chromite by weight. The composition of the catalyst may be varied using yappropriate amounts of ammonium dichrornate and zinc nitrate as the starting materials.

The naphtha used in the process of the present inven-4 tion may be derived from any suitable source such `as the fractional distillation of a crude petroleum oil or thermally or catalytically cracked stocks. The naphtha is then fractionated into a light fraction and a heavy fraction. When cracked naphthas are used it is desirable to make the separation at a temperature of about 20G-225 F. When straight run naphtha is used the separation is made at a point between about 200 and 280 F. depending on the source of the crude. Generally, it is preferred to make the separation at a temperature which results in the bulk of the nonearomatizable compounds being removed in the light fraction.

The treatment of the heavy fraction with the Zinc oxide-zinc chromite catalyst is preferably accomplished in the presence of hydrogen. Temperatures may range from 700 to 1100 F., a preferred range being 900 to 1050D F. Liquid hourly space velocities, that is volumes of feed per hour per volume of catalyst, are preferably 0.5-1.0 `although space velocities of 0.1-5.0 may be used. The pressure may range from `atmospheric to 1000 p.s.i.g. or higher. Pressures from *atmospheric to 600' p.s.i.g. have been found to be satisfactory. Hydrogen flow rates may range up to 10,000 lcubic feet per barrel of feed.

The light fraction may be combined directly with the treated heavy fraction or it may be subjected to additional treatment to increase its octane number and then combined with the treated heavy fraction. Such additional treatment comprises a desulfurization step `and an isomerization step. lf the light fraction consists, for the most part, of paraiiinic hydrocarbons, or if the sulfur is present as mercaptans, it is satisfactory to effect desulfurization by means of a caustic wash. If the light fraction contains ring sulfur compounds, however, it is preferable to remove the sulfur by treating the light fraction with hydrogen in the presence of a sulfur resistantcatalyst such as cobalt molydbate on alumina. This latter treatment may also be effected under such conditions that, if any oleiins are present in the light fraction, they are hydrogenated to parafns.

The desulfurized light fraction may ythen be passed to a separator Where the isopar-ains are separated from the normal paraflins. When the light fraction contains large amounts of C5 hydrocarbons it may be topped and the isopentane separated from the normal pentanes by fractional distillation. When the light fraction contains large amounts of hydrocarbonsvother than C5 hydrooarbons the separation of straight chain from nonstraight chain hydrocarbons is effected preferably'by a solid adsorbent which selectively absorbs straight chain hydrocarbons.

Any solid adsorbent which selectively adsorbs straight chain hydrocarbons to the substantial exclusion of nonstraight chain hydrocarbons can be employed in the process of this invention for the treatment of the light fraction. lt is preferred, however, to employ as the adsorbent certain natural or synthetic zeolites or aluminosilicates, such as a calcium alumino-silicate, which exhibit 'hydrocarbons in the the properties of a molecular sieve, that is, adsorbents made up of porous matter or crystals wherein the pores are of molecular dimension and are of uniform size. A particularly suitable solid adsorbent for the adsorption of straight chain hydrocarbons to the substantial exclusion of non-straight chain hydrocarbons is a calcium aluminosilicate manufactured by Linde Air Products Company :and designated Linde Type A molecular sieve. The crystals of this particular calcium alumino-silicate, apparently actually a sodium calcium alumino-silicate, have a pore size cr pore diameter of about 5 Angstrom units, a pore size suicient to admit straight chain hydrocarbons such as the n-paraiins, to the substantial exclusion of the non-straight chain hydrocarbons, such as the naphthenic, aromatic, isoparifiinic, and isoolelinic hydrocarbons.

Other solid selective adsorbents may be employed. For example, it is contemplated that adsorbents having the property of selectively adsorbing straight chain hydrocarbons to the substantial exclusion of non-straight chain manner of a molecular sieve may be obtained Eby suitable treatment of various oxide gels, especially metal oxide gels of the polyvalent amphoteric metal oxides.

Other suitable selective adsorbents are known a-nd include the synthetic and natural zeolites which, when dehydrated, may be described as crystalline zeolites having a rigid three dimensional anionic network having interstitial dimensions sulhciently large to adsorb straight chain hydrocarbons but suiiiciently small to exclude the nonstraight chain hydrocarbons. The naturally occurring zeolite, chabazite, exhibits such desirable properties. Another suitable naturally occurring zeolite is analcite, NaAlSi2O6.H2O, which, when dehydrated, and when all or part of the sodium is replaced -by an alkaline earth metal such as calcium, yields a material which may be represented by the formula (Ca,Na)Al2Si4O12.2H2O and which, after suitable conditioning, will adsorb straight chain hydrocarbons to the substantial exclusion olf nonstraight chain hydrocarbons. Naturally occurring or `synthetically prepared phacolite, -gmelinite, harmotome and the like or suitable modilications of these products by base exchange are also applicable in the practice of this invention.

Other solid adsorbents which selectively adsorb straight chain hydrocarbons, such as n-paraiins and n-olefins, to the substantial exclusion of non-straight chain hydrocarbons are known.

In the selective adsorption step, the low boiling fraction is contacted with a solid adsorbent such as an alkaline earth metal alumino-silicate, preferably a calcium alumino-silicate, to eiect the adsorption separation of straight chain hydrocarbons therefrom. Adsorption conditions in the adsorber may include a temperature 4within the range of about 200 to 800 F., and a pressure in the range of about to 700 pounds per square inch gauge. It is preferred to maintain the adsorption conditions such that the fraction undergoing treatment is in the vapor phase. After contact with the adsorber to ehect the adsorption of straight chain hydrocarbons, the treated fraction is separated substantially free of straight chain hydrocarbons.

On completion of the adsorption operation, the adsorber is subjected to desorption conditions to effect the removal of the adsorbed straight chain hydrocarbons. Suitable desorption conditions include a temperature in the range of about 500 to 900 and a pressure in the range of -about l5 to 100 pounds per square inch gauge. It is preferred to carry out the desorption operation under such conditions that the straight chain hydrocarbons are desorbed or recovered in the vapor phase. Desorption of the straight chain hydrocarbons is facilitated by the introduction of a stripping medium to displace the desorbed straight chain hydrocarbons from the `adsorption zone. Gases suitable as stripping media include hydrogen, nitrogen,

4 carbon monoxide, carbon dioxide, steam, normally gasecus hydrocarbons, and low molecular weight hydrocarbons such as isopentane. Reformer oft-gases comprising hydrogen and small quantities of normally gaseous hydrocarbons are suitable.

The separated isoparathns are combined with the treated heavy naphtha and the normal parains are passed to an isomerization unit where they are contacted with an isomerization catalyst such as aluminum chloride, aluminum bromide, platinum or palladium on a suitable sup- .,port. The elucnt from the isomerization unit is returned to the separator where the normal parans are separated from the isoparaflins.

The invention will be more clearly understood from the following description of the `accompanying drawing which illustrates diagrannnatically a liow plan in accordance with the present invention.

A full range naphtha is introduced through line 1 into dash tower 2 Where it is separated into a light fraction and a heavy fraction. The heavy fraction is withdrawn through line 3 and with hydrogen introduced from line 4 is fed to reactor 5 which contains a zinc oxide-zinc chromite catalyst. The products from reactor 5 are passed through line 6 to degasitier 7 Ifrom which the treated heavy fraction is Withdrawn through line 9 Aand a gas containing substantial amounts of hydrogen is recycled to lreactor 5 via line 8 and line 3. When there is a net production of hydrogen, as, for example when there is a high ratio of aromatiza'ble naphthenes to oletns in the charge to reactor 5, excess hydrogen can be diverted to reactor 18 through lines 8, 3S, 36 and 17, or isomerization lunit 26 through lines 8, 35, 37 and 25.

The light fraction is removed vfrom flash tower 2 through line 10 `and may be combined with the treated heavy naphtha through line 11. Optionally the light naphtha may be introduced to scrubber 13 through line 12 where it is contacted with a caustic wash and the desulfurized light naphtha withdrawn through line 14. Alternatively, if the light naphtha contains ring sulfur compounds, Vit is mixed with hydrogen from line 16 and passed through `line 17 to reactor 18. In reactor 18 the hydrogen-hydrocarbon mixture is contacted with a desul-furization catalyst Vsuch as cobalt molybdate on alumina to convert the sulfur compounds to hydrogen sulfide and, if oleiins are present, to hydrogenate at least a portion of the oleiins. The eiliuent from reactor 18 passes through line 19 to degasilier 20. The gases are removed through line 21 and introduced to scrubber 22 where they are treated for the removal of H28 from the hydrogen as for example by being scrubbed with a diethanolamine solution. The separated hydrogen is recycled through line 23 and HZS is removed from the system through line 24.

Light naphtha withdrawn from degasiiier 20 through line 33 or from scrubber 13 is passed through line l14 and introduced into separator 15 where the straight chain hydrocarbons are separated from the non-straight chain hydrocarbons. 'Ihe non-straight chain hydrocarbons are removed through line 31 and combined with the treated heavy fraction in line 9. The straight chain hydrocarbons Iare withdrawn from separator 15 through line 25 and together with hydrogen from line B2 are introduced into isomerization unit 26 where a portion of the straight chain hydrocarbons are isomerized. The eiiluent from the isomerization unit 26 is passed through line 28 to degasit'ier 29 where a hydrogen containing gas is separated from the eiuent and recycled to isomerization unit 26 through lines 27 and l25. The hydrocarbons are then returned from degasifier 29 to separator 15 through lines 30 and 14. Optionally, a portion or all of the hydrocarbons from degasilier 29 may be combined with the treated heavy fraction in line 9 through line 34.

The following examples illustrating the invention are for illustrative purposes only.

EXAMPLE YI A catalytically cracked -naphtha having ASTM vResearch Octane Nos. of 91 clear and 96 leaded'was subjected to ash distillation to remove a light fraction havingr the following characteristics:

Table I Boiling range F. 110-225 YHydrocarbon type analysis:

Aromatics A-.. ;percent Olens v do 60 Saturates do 35 ASTM Research' Octane No.:

Clear 93.8 -l-3 cc. TEL/gal 99.2

The overhead mounted to approximately 66% of the charge.

- The heavy fraction was passed over a catalyst containing 26% zinc oxide and 74% zinc chromite at 1000 F., a space velocity of 0.2 v./v./hr. and atmospheric pressure. The follovn'ng table shows a comparison of the charge and the product:

g l Wiese scale.

The combined light fraction and treated heavy fraction yields a product having ASIM Research Octane Nos. of 95.9 clear and 99.7 leaded in an overall yield of 93.8%.

EXAMPLE 1I The same charge used in Example I was ilashed under the same conditions. The heavy fraction was then treated over the zinc oxide-zinc chromite catalyst at 1000" F., 400 p.s.i.g., a space velocity of 1.0 v./v./hr. and a hydrogen recycle rate of 3000 cu. ft./ bbl. The `following results were obtained:

cnl Table IV Tlmeon stream (hrs.). A Charge 4 8 12 16 Hydrocarbon Type Analysis:

Aromatics... 23 62 54 48 46 OleflDS.-. 25 9 13 14 13 Saturates. 52 29 33 38 41 ASTM Distillation Range:

IBP 218 128 133 116 n 112 250 218 211 n 2714- 202 29() 290 285 284 453 456 442 438 Sulfur is removed from the light fraction by treatment with a cobalt molybdate on alumina catalyst at 600 IF., and" 500 p.s.i.g. in the presence of added hydrogen, the normally liquid products separated from the normally gaseous products and the liquid products'thcn passed through a selective adsorbent which retains the normal paraflins. The unadsorbed isoparatlins are combined with the treated heavyfraction and the normal parains after being desorbed, vare contacted with a platinum 'isomeriz'ation catalyst at a temperature of 22S-800 and a pressure of 500 p.s.i.g. in the presence of added hydrogen. When the hydrogen-containing gas has been removed, the isomerization product is also combined with `the treated heavy fraction. The overall upgrading is shown in the following table:

Table V Naphtha Final Charge Product Hydrocarbon type analysis:

Aromatics 17 30 Oleiins 32 7 e Saturates. 51 63 ASTM Research Octane No.:

Clear 76. O 93. 8 +3 ce. TEL/gal 88.0 98.4

EXAMPLE 1V A straight run naphtha having ASTM Research Nos. of 56.2 clear and 76.0 leaded was separated into light and heavy fractions the cut being made at 200 F. The heavy fraction was passed over ,the zinc oxidezinc chrornite catalyst at a temperature Vof 1050lo P., a space velocity of 1.0 v./v./hr., a pressure of 400 p.s.i.g. 'and a hydrogen recycle rate of 2000 cu. ft./bbl. The results obtained are shown inthe following table:

Table III Table Vl l. Time on stream (hrs.) Charge s 9 15 Tune on mem (hls') Charge 4 20 ge 55 ASTM Research Octane No.: ASTM R a h o t N Crear 87.9 1100.42 99.1 018 52.8 08.8 95.1 95.8 +3 ce.TEL/gal 93.1 103. 51 1100.55 100-55 +3 ee'rEL/gai 73.1 1103.11 99.2 100.0

1 Wiese scale.

The combined light fraction and treated heavy fraction gives a product having ATSM Research Octane Nos. of 95.0 clear, 99.9 leaded in an overall yield of 93.6%.

This treatment also results in a reduction of the sulfur content from 0.1% in the charge to 0.005% in the product.

EXAMPLE HI 1 Wiese scale.

rThe light fraction is treated in the same manner as in n Example Ill with the exception that the sulfur compounds are removed by scrubbing with a caustic solution. The overall upgrading is shown in the following table comparing the full-range charge naphtha with the combined final product.

Table VII Charge Product ASTM Research Octane No.:

Clear 56. 2 95.9 +3 cc. TEL/gal 76. 0 100.0

Various modications may be made of the abovedescribed process, for example, the light fraction may be oleiins present in said heavy fraction and subjected to a hydrogenation treatment and after removal of the excess hydrogen and gases may be combined d1- rectly with the treated heavy fraction. The treated heavy fraction may also be upgraded further by additional treatment with a selective solvent whereby the aromatic compounds present are removed from. the parainic compounds and the paraliinic compounds recycled for additional treatment with the zinc oxide-zinc chromite catalyst` It is also contemplated that mixtures of naphthas from various sources may be used as the charge in which case it may be advisable to fractionate the light fraction, passing one portion to the caustic scrubber and another portion to the hydrodesulfurization reactor.

Other modifications and variations of the invention may be made without departing from the spirit and scope thereof and only such `limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for upgrading a naphtha which comprises separating said naphtha into alight traction having a nal boiling point between 200 F. and 280 F. and a heavy fraction having an initial boiling point between 200 F. and 280 F., contacting the heavy fraction with a catalyst comprising zinc oxide and zinc chromite and containing between about and 90% zinc oxide based on the combined weights of zine oxide and zine chromite at a temperature between about 900-1050 F., a pressure between about 400 and 600 p.s.i.g. in the presence of added hydrogen to elect the substantial saturation of to e-ect the substantial production of aromatic hydrocarbons, desulfurizing the light naphtha fraction, introducing the de- .sulfurized light naphtha fraction to a separation zone wherein straight chain hydrocarbons are separated from non-straight chain hydrocarbons, combining the separated non-straight chain hydrocarbons with the treated heavy fraction,y contacting the straight: chain hydrocarbons in an somerization zone with an isomerizaton catalyst and returning the products of said isomerization zone to said separation zone.

2. The process of claim l straight run naphtha.

3. The process of claim 1 in which the naphtha is a thermally cracked naphtha.

4. A process for the production of a motor fuel of high octane number which comprises separating a naphtha into a light fraction boiling below about 225 F. and

in which the naphtha is a 8 a heavy fraction, contacting said heavy fraction with a zinc oxide-zinc chromite catalyst containing between 10 and zinc oxide based on the combined weights of zinc oxide and zincy chromite at a temperature between A900 and 1050 F., a liquid hourly space velocity between 0.1 and 1 volume of feed per volume of catalyst per hour and a pressure between about 400 and 600 p.s.i.g. in the presence of added hydrogen to effect the substantial saturation of oleiins present in said heavy fraction and to eifect the substantial production of aromatic hydrocarbons, separating from the normally liquid portionof the product a hydrogen containing gas, recyclinga first portion of said hydrogen containing gasto the zinc oxidezinc chromite catalyst reaction zone, combining a second portion of said hydrogen containing gas with said light fraction and passing the combined stream into contact with a desulfurization catalyst to eiect desulfurization of said light fraction, passing the desulfurized product into contact with a selective adsorbent to elect separation of the straight chain hydrocarbons from the non-straight chain hydrocarbons, combining the separated straight chain hydrocarbons with a third portion of said hydro gen containing gas separatedfrom the zinc oxidelzinc chromite catalyst reaction product and introducing the combined straight chainhydrocarbons-hydrogen stream into an isomerization zone containing Ia platinum isomerization catalyst at a temperature between about 725 and 800 F., separating gaseous material from the normally liquid isomerization zone reaction product and combining the treated heavy fraction, the normally liquid isomer-ization zone reaction product and the separated non-straight chain hydrocarbons to produce a motor fuel of high octane number.

References Cited in the tile of this patent 

1. A PROCESS FOR UPGRADING A NAPHTHA WHICH COMPRISES SEPARATING SAID NAPHTHA INTO A LIGHT FRACTION HAVING A FINAL BOILING POINT BETWEEN 200*F. AND 280*F. AND A HEAVY FRACTION HAVING AN INITIAL BOILING POINT BETWEEN 200*F. AND 280*F., CONTACTING THE HEAVY FRACTION WITH A CATALYST COMPRISING ZINC OXIDE AND ZINC CHROMITE AND CONTAINING BETWEEN ABOUT 10 AND 90% ZINC OXIDE BASED ON THE COMBINED WEIGHTS OF ZINC OXIDE AND ZINC CHROMITE AT A TEMPERATURE BETWEEN ABOUT 900-1050*F., A PRESSURE BETWEEN ABOUT 400 AND 600 P.S.I.G. IN THE PRESENCE OF ADDED HYDROGEN TO EFFECT THE SUBSTANTIAL SATURATION OF OLEFINS PRESENT IN SAID HEAVY FRACTION AND TO EFFECT THE SUBSTANTIAL PRODUCTION OF AROMATIC HYDROCARBONS, DESULFURIZING THE LIGHT NAPHTHA FRACTION, INTRODUCING THE DESULFURIZED LIGHT NAPHTHA FRACTION TO A SEPARATION ZONE WHEREIN STRAIGHT CHAIN HYDROCARBONS ARE SEPARATED FROM NON-STRAIGHT CHAIN HYDROCARBONS, COMBINING THE SEPARATED NON-STRAIGHT CHAIN HYDROCARBONS WITH THE TREATED HEAVY FRACTION, CONTACTING THE STRAIGHT CHAIN HYDROCARBONS IN AN ISOMERIZATION ZONE WITH AN ISOMERIZATION CATALYST AND RETURNING THE PRODUCTS OF SAID ISOMERIZATION ZONE TO SAID SEPARATION ZONE. 